The field of the present invention is electronic data processing apparatuses and more specifically to the so called scientific calculators. Scientific calculators are typically hand held or desk top devices which include a manually actuable keyboard for receiving input data and operational commands from the operator and a visual display for communicating the results to the operator. A more recent development is the provision of an alphanumeric display which may be employed to display the sequence of operations in an inputted equation in order that the operator may check this equation for accuracy and possible revision prior to evaluation.
The increasing complexity of these scientific calculators together with the trend toward providing alphanumeric equation displays has provided impetus to the search for more user friendly entry formats and operational sequences. The previous calculators employed a so called chain arithmetic format, in which each operation is performed in the order in which it is entered, regardless of the relative hierarchical ranks of such operations in written form. Later calculators, as exemplified in U.S. Pat. No. 4,208,720 entitled "Calculator with Algebraic Operation System" by Herman W. Harrison, provided operation upon entered command sequences based upon the hierarchical rank of the entered operations as modified by open and closed parenthesis. Other solutions to this problem include the reverse Polish notation which is relatively efficient in terms of key strokes required for evaluation of most equations, however it has the disadvantage of requiring a completely different approach for entry than the manner in which an equation is ordinarily written.
One major problem with an alphanumeric display of an entered equation is that, typically, such alphanumeric displays do not have any provision for more than a single line of characters. Therefore, it is difficult to easily represent exponentiation in the written manner in which the operator is most familiar. Typically such calculators would employ a YX character to indicate that the numeric data preceeding this character is to be raised to the power of the numeric data following this character. Although such a character unambiguously depicts this exponentiation, this character is conceptually removed from the superscript notation employed in written equations.
A further problem occurs with the prior art calculators of the scientific type in that they typically are not constructed to perform implied multiplication. Implied multiplication is often used in written equations between numbers, variables, functions and open and closed parenthesis. Provision in the operating system of a scientific calculator to evaluate and properly perform implied multiplication would typically reduce the number of keystrokes required for entry of equations.
Scientific calculators differ in the manner in which the operand is entered for unary operations. Unary operations are operations which require a single operand such as the trigonometric functions of sine, cosine and tangent and the common and natural logarithms. Early scientific calculators typically performed such unary operations immediately when entered using the currently displayed number as the operand. This differs from the typical written representation of such functions in which the operand generally follows the function. Some scientific calculators, particularly those in which alphanumeric equation display is provided, require that the operand be entered following the function in the manner in which these functions are typically written. Because of this split between the manner in which the operand and the operator are entered, it is often confusing to a user who switches between one machine and another. This is because the user will often not know the particular operating sequence of that machine without experimentation.